[单项选择]Both Boeing and Airbus have trumpeted the efficiency of their newest aircraft, the 787 and A350 respectively. Their clever designs and lightweight composites certainly make a difference. But a group of researchers at Stanford University, led by Ilan Kroo, has suggested that airlines could take a more naturalistic approach to cutting jet-fuel use, and it would not require them to buy new aircraft.
The answer, says Dr. Kroo, lies with birds. Since 1914, and a seminal paper by a German researcher called Carl Wieselsberger, scientists have known that birds flying in formation—a V-shape, echelon or otherwise—expend less energy. The air flowing over a bird’s wings curls upwards behind the wingtips, a phenomenon known as upwash. Other birds flying in the upwash experience reduced drag, and spend less energy propelling themselves. Peter Lissaman, an aeronautics expert who was formerly at Caltech and the University of Southern California, has suggested that a formation of 25 birds might en
A. Three passengers were in the most favourable positions during the experiment.
B. 15% less fuel reduction in carbon-dioxide output and nitrogen-oxide emissions during flying.
C. Kroo and his team conducted their experiments in Los Angeles, San Francisco, Las Vegas, Utah and London.
D. Air crafts can occasionally swap places to turn in the most favourable positions as well as birds.